This application corresponds to Japanese Patent Application No. 10-339766, filed on Nov. 30, 1998, which is hereby incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a technique for manufacturing electronic parts in which a plated film is formed on an external electrode of an electronic part, such as, for example, a monolithic capacitor or the like, to form an external electrode. More particularly, the present invention relates to a technique for manufacturing an electronic part by barrel plating using a barrel into which conductive elements are mixed with electronic parts.
2. Description of the Related Art
In a chip type electronic part, such as, for example, a monolithic capacitor or the like, the surface of an external electrode of the electronic part comprises a plated film. The film has excellent solderability, which facilitates the mounting of the electronic part. In forming such a plated film, barrel plating has been frequently used.
The barrel plating technique uses a hexagonal cylindrical barrel 51 as shown in the cross-sectional view in FIG. 4(a). The barrel plating technique is performed by the following process. Chip type electronic parts to be plated are disposed in the barrel 51 together with numerous conductive elements. The barrel 51 is rotated. Electric conduction is affected between a negative pole bar 60 introduced in the barrel 51 and a positive pole of metal disposed in plating liquid outside of the barrel 51 (not shown). The ionized metal fused from the positive pole of the metal attaches to surfaces of the electrodes of the electronic parts that are charged with a negative electric potential by the negative pole bar 60 and the conductive elements. In this manner, the plating layer is formed. The conductive elements 51 collectively function as an electric medium which distributes the negative electric potential from the negative pole bar 60 uniformly over all the chip type electronic parts dispersed in the barrel 51.
More specifically, electronic parts (not shown) having external electrodes to be plated and numerous spherical conductive elements 52 are placed in the barrel 51, and electroplating is carried out in the barrel 51 while the barrel is rotated around the axis thereof in the direction of arrow A shown in FIGS. 4(a) and 4(b). The spherical conductive elements 52 function as electrodes for applying a voltage to the external electrodes, and also function as agitators which agitate the electronic parts in the barrel 51. That is, the rotation of the barrel 51 causes agitation of the conductive elements 52 and the electronic parts during electroplating, thereby permitting the formation of plated films having a uniform thickness on the external electrodes of the electronic parts.
Using conductive elements 52 that are spherical may beneficially decrease variations in thickness of the plated films on the external electrodes of many electronic parts placed in the barrel 51. This effect is promoted by the reduced variations in shape and dimensions of the conductive elements 52.
However, a problem occurs when the barrel 51 is rotated in the direction of arrow A, causing the conductive elements 52 to slide on the inner wall surface of the barrel 51. The conductive elements 52 and the electronic parts cannot be sufficiently agitated. More specifically, as shown in FIG. 4(b), when the barrel 51 is rotated in the direction of arrow A, many conductive elements 52 and the electronic parts (not shown) situated on the side 51a of the barrel 51 tend to move downward when the side 51a moves upward. In this case, because the conductive elements 52 have a spherical shape, when the barrel 51 is rotated in the direction A such that the side 51b moves into the position of side 51a, the conductive elements 52 and the electronic parts tend to slide down the side 51a, as shown by arrow B, and then move to the next side 51b without producing much agitation movement. Therefore, the conductive elements 52 and the electronic parts are not sufficiently agitated.
An increase in the diameter of the conductive elements 52 sometimes causes insufficient contact between the electronic parts and the conductive elements 52. More specifically, the conductive elements 52 have diameters which are not very large, as shown in FIG. 5. As such, the spaces between adjacent conductive elements 52 are small, thereby causing secure contact between the external electrodes 53 of the electronic parts and the conductive elements 52. On the other hand, with conductive elements having excessively large diameters, as shown in FIG. 6, the spaces C between adjacent conductive elements 52 are increased, decreasing the probability of contact between the external electrodes 53 of the electronic parts situated in the spaces C and the conductive elements 52. Therefore, it is necessary to prepare conductive elements 52 which have an appropriate diameter relative to the size of the electronic parts which are to be plated.
Thus, the above-described conventional method of manufacturing electronic parts using barrel plating can produce variations in thickness of the formed plated films due to sliding of the conductive elements 52 and parts on the side 51a of the barrel 51, the small size of electronic parts relative to the conductive elements 52, etc. These factors can cause variations in solderability and consequent soldering defects.
Accordingly, it is an object of the present invention to provide a method of manufacturing electronic parts including a plating technique capable of solving the problems of the above-described conventional technique. Namely, it is an object of the present invention to provide plated films having reduced thickness variations formed on external electrodes of electronic parts of various sizes.
In order to achieve the object of the present invention, a method of manufacturing electronic parts is provided, comprising disposing a plurality of deformed (e.g, non-spherical) conductive elements in a plating barrel, disposing a plurality of electronic parts in the plating barrel, and rotating the plating barrel to form a plated film on the external electrodes of the electronic parts.
The maximum dimension of a conductive element is defined as the length of the longest line segment which passes through a central region of the conductive element. The minimum dimension of a conductive element is defined as the length of the shortest line segment which passes through the central region of the conductive element. The deformed conductive elements preferably have a ratio of the maximum dimension to the minimum dimension within the range of about 1.1 to 3.0.
Further, in the present invention, the deformed conductive elements can be used in combination with spherical conductive elements.
The present invention also pertains to a combination comprising a barrel for use in plating a film on external electrodes of the electronic parts, and a plurality of non-spherical conductive elements disposed in the barrel for applying electric voltage to the electronic parts.